When petroleum transporting pipes are laid under water it is necessary to coat them with several inches of concrete, usually reinforced with wire, to prevent the pipes from floating to the surface. If the pipeline is damaged, it is necessary to remove this concrete weight coat before repairs can be made to the pipeline itself.
Heretofore, removal of the concrete coat has been difficult, dangerous and slow. A common method of removal was for a diver to fracture the concrete with a pneumatic jack hammer and manually pry loose the fractured segments with a large bar. Concrete removal proceeded very slowly, with the diver often working at a depth where exertion was a major handicap. There was also the risk of injury from the jack hammer and the sharp edges of the reinforcing wire. Moreover, since the diver had to position himself adjacent to, or below the pipe, concrete fragments could strike or trap him on the sea bed. Operation of the jack hammer also reduced visibility by agitating silt on the sea bed, adding to the hazard by rendering the diver essentially blind while operating unwieldy and potentially dangerous equipment. Use of the jack hammer under these conditions also presented the risk of additional damage to pipelines in the form of nicks, dents, gouges, and, most seriously, linear splitting, caused by the pneumatic chisel.
Another method of weight coat removal, disclosed in U.S. Pat. Nos. 3,933,519 and 4,229,121 employs high pressure water jets. The latter patent discloses a pair of opposed jets affixed to a crescent which is mechanically oscillated about the axis of the pipeline. The crescent does not contact the pipeline and is supported and moved longitudinally along the pipeline by a boom and track. However, the automated equipment described in these patents is mechanically complex, bulky and obviously expensive to construct and maintain. In addition, the use of hydraulic jets to efficiently blast the concrete coating from the pipe will stir up the bottom silt and further reduce what is already generally very poor visibility.
The use of explosive charges, both of the blanket and linear type, is also well known in the art. The use of explosives presents obvious and special dangers, requires the skills and care of trained and experienced experts and produces results which are not always predictable.
It is therefore an object of this invention to provide an improved method and apparatus for removing concrete weight coats that is efficient, safe and economical to construct and operate.
It is another object of the invention to provide a method and apparatus that is capable of operation by a single diver and the practice of which will not contribute significantly to a reduction in the visibility in the area where the work is being performed.
It is yet another object of this invention to provide a method and apparatus for removing a concrete weight coat from a pipeline without the risk of further damage to the pipeline.
It is a further object of the invention to provide a method and apparatus for concrete weight coat removal that can be practiced with minimum exertion by the diver and one where the diver is able to control the movement and activation of the removal means directly, or by transmitted voice commands, or other signals, to a surface crew.